Tilting chairs usually contain some mechanism which provides a lock or stop, limiting the extent of tilting of the chair seat surface and/or of the chair back, together or independently, with respect to a rest position. European Published Patent Application No. EP-A-0 001 846, Flum, describes a tilting chair which permits blocking tilting of the chair back in various positions. The construction permits fine adjustment. When the chair back has been set to a certain tilted position, it cannot be tilted anymore forwardly or backwardly; in other words, the tilt or inclination of the chair back is fixed. If the user wishes to rock in the chair, the blocking or locking mechanism can be unlocked. If the user, then, rises from the chair, the back will be moved under spring pressure to its foremost or rest position. To reset a desirable angle of the chair back, then, requires first moving the chair back to the tilted position desired, and then, again, locking or blocking the chair back in that particular position.
Constant resetting of the predetermined and usually most comfortable inclination or tilt of the chair back is undesirable and annoying to the user, particularly if an initial adjustment by the user does not result in a comfortable tilt or inclination of the back, so that readjustment is necessary--which readjustment is lost as soon as the user wishes to rock on the chair.
The chair described in the European Patent Application Flum locks the inclination of the back in position by bolts which engage in an apertured plate. It is also possible to lock the inclination of the back in position by blocking a gas spring--see German Patent No. 27 33 322. Gas springs are widely used in connection with chair construction, since they can be easily employed not only as springs but, additionally, as a stepless, continuously variable positioning element, in that the position of the sprung structure can be determined by blocking the gas spring. The gas spring includes a valve and, by closing the valve, the spring can be hydraulically or pneumatically locked or unlocked in any specific position. The chair described in German Patent No. 27 33 322 thus permits placing the chair back in any desired position. Upon unlocking of the gas spring, rocking movement of the chair is possible. As soon as the user leaves the chair, however, for example rises, the now unlocked gas spring will move the back in its foremost or rest position so that, if the user wishes to use the chair again in a comfortable position, the gas spring must first be compressed and then locked in position, with possible adjustment if a comfortable position is not immediately found. The result, as far as the user is concerned, is similar to that of the chair described in the European Patent Application Flum.